Re: RAID 10 far and offset on-disk layouts

[Gionatan Danti <g.danti@assyoma.it>]

>> Ok, so let recap:
>>
>> 1) FAR layout is the one depicted by SuSe documentation, while the
>> Wikipedia entry is wrong
>
> Yes.
>
>>
>> 2) MD _can_ produce a FAR layout as depicted by Wikipedia, but we don't
>> know how the user-space mdadm tool call it (maybe it is not implemented
>> yet?)
>
> Yes.  Not implemented yet.
>
>>
>> 3) There are any reasons why FAR and OFFSET layout scramble data in this
>> manner, coupling any disk with two more disks? It was done for
>> simplicity, or I am missing something?
>
> It just seemed the easiest thing to do at the time.
>
>>
>> 4) you confirm that currently we can _not_ create a FAR layout as the
>> one depicted by wikipedia by no means? What about OFFSET layout?
>
> You certainly can created the FAR layout depicted on wikipedia, e.g. by
> binary-editing the metadata on some devices, or writing some code which does
> that for you.  It requires flipping one bit in the metadata and updating the
> checksum.  You can probably even to it by writing something appropriate into
> some sysfs files.
> But mdadm cannot do it yet.
> Ditto for the new OFFSET layout.
> (The old offset layout can be created with "--layout=o2").
>
> NeilBrown
>

All clear now :)

Thank you very much Neil.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8